The transmission of messages and documents by facsimile transceivers (fax machines) is becoming an increasingly popular and widespread practice. As a further development, it is not necessary for an actual fax machine to exist at either the source or the destination of the message transaction. A so-called "fax modem" may take the place of the fax machine at either or both locations. A fax modem connects to a telephone line on one side and to a computer on the other. On the telephone side it can both send and receive audio signals in one of the CCITT formats that represent an image undergoing facsimile transmission. On the computer side it either sends or receives a stream of eight-bit bytes of compressed data representing an image. A suitable application program running on the computer either converts an incoming byte stream to a bit-mapped image for display on a monitor or other output device, or converts a displayed image to its corresponding outgoing byte stream. Such an application program (together with its associated computer) may be terms a "fax viewer."
In a large facility it is typical to find many fax modems connected on the phone line side to some number of phone lines, and connected on the computer side to a single computer running a program called (in association with the computer) a "fax server". In turn, the fax server is connected to a Local Area Network (LAN), wide area network, or other Electronic mail (E-mail) system. (Hereinafter, we shall simply use the term "network" as a synonym for any of the preceding computer-to-computer communication arrangements.) In such a facility there may be several hundred subscribers on the network, each with a fax viewer running on his computer and an assigned fax phone number, but perhaps only five or ten fax modems. Whereas a small business may well be obliged to use an actual subscriber loop per modem (which may be termed "traditional single party service"), a larger facility can arrange for the local phone company to interact with the facility as if it were an exchange in its own right. Then, some level of trunking is provided between the central office of the local phone company and a private branch exchange at the large facility. A well known conventional arrangement allows the allocation of the fax modems to whichever ones of selected (for fax service) phone lines are in use. This arrangement may be termed "direct inward dialing."
With either traditional single party service or direct inward dialing there is a necessary correspondence between the phone number used to dial the destination within the facility and the E-mail address of the intended recipient. If someone wants to send Charlie (who is a useful but wholly fictitious person) a fax, then they must dial Charlie's fax number. To correctly route the received fax the fax server must determine to which phone line the modem receiving Charlie's incoming fax is connected. That information indexes a table of E-mail addresses; Charlie's fax phone number points to Charlie's E-mail address.
While single party service and direct inward dialing work, they are not without a few warts. First, there is the matter of the phone line per user for single party service. To add a user it is necessary to add a phone line, which involves the phone company and added expense. Even with direct inward dialing a proliferation of fax phone numbers could require a change to the level of trunking to maintain adequate service. It would be cheaper and just as useful if a way could be found to use a suitable number of phone lines all representing the same phone number, and answer or select them "in rotation." Second, unless there is a modem per phone line (expensive!), there is the hardware needed to keep track of which phone line is being served by which fax modem. The system would be less expensive if that hardware could be eliminated. Third, there is system administration associated with adding or deleting a user. The table of correspondence between fax phone numbers and E-mail addresses must be kept up to date, or incoming faxes will not be correctly routed.
And while on the subject of warts, it should be noted that a conventional fax server has no way of determining if the received fax message will appear upside down on Charlie's fax viewer. It is usually left to the recipient to turn upside down messages right side up.
The underlaying reason for all these particular warts on the prior art is that the fax server has no way to read the incoming fax message and intelligently base its actions on the contents of the message.